When I started reading No more Mr nice guy I almost immediately realised that I'm a nice guy. Being a nice guy has done really bad things to my life, and this book contains concrete tips and tricks on how to change that outlook on life.
According to the author a "nice guy" is basically pretending to be nice and do whatever others expect of him, while being angry or upset over them not living up to their part of the deal; a deal that the counterparty was never told existed. More or less a different way of describing passive-aggressive behaviour.
The book explains what a nice guy is, and (most importantly) contains exercises for the reader so that he can change his life for the better.
Personally still working on the early exercises, but definitely a life saver. Recommended!